1. Field of the Invention
The present invention relates to an image processing device, method, and program storage medium. In particular, the present invention relates to an image processing device which carries out correction of defective pixels on an image picked-up (captured) by an image pickup element, and to an image processing method which can be applied to the image processing device, and to an image processing program storage medium for causing a computer to execute the image processing.
2. Description of the Related Art
In radiation photography for medical diagnosis, there is known a system which obtains digital radiographic images as follows: radiation which has been transmitted through a subject is irradiated onto a radiographic image detector equipped with a photoelectric converting layer which is sensitive to radiation, the charges which are accumulated at the radiographic image detector in accordance with the radiation dose irradiated onto the radiographic image detector are read-out per pixel as electrical signals, and the read-out electrical signals are converted into digital data. In radiographic image detectors of this type of system, there are cases in which pixels at which output corresponding to the irradiated radiation dose cannot be obtained (called “defective pixels”) arise due to, for example, deterioration due to the irradiation of the radiation, poor contact of electrical wires, or the like. Therefore, defective pixels of a radiographic image detector are detected in advance, and defective pixel correction, which corrects the luminance or density of the image portions corresponding to the defective pixels on the basis of the results of detection of the defective pixels, is carried out on the radiographic image obtained by the radiation photography.
In relation to the above-described defective pixel correction, Japanese Patent Application Laid-Open (JP-A) No. 2001-8198 discloses a technique in which the average and the standard deviation of the pixel values of the entire image region or an arbitrary region of image information are computed, and, for each pixel of the image information, it is determined whether or not the absolute value of the difference between an object pixel value and the average is greater than the results of multiplication of the standard deviation and a magnification designated in advance, and, if greater, the object pixel is determined to be a defective pixel.
Further, JP-A No. 2005-167773 discloses a technique in which line defects are extracted from an image for defect extraction, and the line defects of the image for defect extraction are corrected by using the extracted line defect information, and either defective pixels are extracted by using the corrected image for defect extraction, or pixel defects are extracted without using the pixel values corresponding to the extracted line defects.
Pixel defects of an image pickup element such as a radiographic image detector can be broadly classified into pixel defects which are formed by a single or a small number of defective pixels being distributed in dot form (called “point defects”), and pixels defects which are formed by plural defective pixels being distributed rectilinearly (called “line defects”). Note that point defects arise mainly due to deterioration due to the irradiation of radiation, whereas line defects arise mainly due to poor contact of electrical wires. Further, as compared with point defects, line defects are easy to recognize visually even if the difference in luminance or the like between them and the surrounding pixels is small.
In regard to this point, in the technique of JP-A No. 2001-8198, when detecting (extracting) pixel defects, detection is carried out without differentiating between the aforementioned point defects and line defects. Therefore, in the technique of JP-A No. 2001-8198, when the threshold value for detection is set such that line defects, which are easily visually recognized, can be reliably detected, at regions other than the pixel defects of the radiographic image detector, noise which is superimposed on the radiographic image also is detected as point defects. Accordingly, the accuracy of detecting and correcting pixel defects deteriorates.
On the other hand, in the technique of JP-A No. 2005-167773, after line defects are detected, detection of point defects is carried out by using an image in which the detected line defects are corrected. Therefore, much time is required until the detection of point defects and line defects is completed. Further, in the technique of JP-A No. 2005-167773, processing becomes complex in a case in which point defects are detected without using the pixel values corresponding to the detected line defects.